1. Field of the Invention
The invention relates to an in-plane switching mode liquid crystal display (IPS-LCD), and more particularly, to an IPS-LCD with a higher opening ratio.
2. Description of the Prior Art
Since the LCD has the advantages of portability, low power consumption, and low radiation, the LCD has been widely used in various portable information products, such as notebooks, personal digital assistants (PDA), video cameras, and etc. Furthermore, the LCD even has a potential to replace the CRT monitor or the television gradually.
The operation theory of an LCD is to control the light amount passing through the liquid crystal layer by various arrangements of liquid crystal molecules and control the polarization and refraction of light beams to perform colorful images. There is a serious limitation in application for a conventional twist nematic (TN) LCD and a conventional super-twisted nematic (STN) for they have very narrow view angles because they are both affected by the structures and optic characteristics of liquid crystal molecules. Therefore the manufacturers are devoted to develop LCDs with new structures that can provide wider view angles. Currently an IPS-LCD is developed to solve the problem of narrow view angle of a conventional IN-LCD.
FIG. 1 is a section view of an IPS-LCD 10 according to the prior art. FIG. 2 is a top view of a lower substrate 14 of the IPS-LCD 10 shown in FIG. 1. Referring to FIG. 1 and FIG. 2, the IPS-LCD 10 comprises an upper substrate 12, a lower substrate 14 formed in parallel with and opposite to the upper substrate 12, a plurality of scan lines 16 and a plurality of data lines 18 arranged perpendicular to the scan lines 16 to form a pixel matrix, a plurality of first electrodes 20 and a plurality of second electrodes 22 on the lower substrate 14, an insulation layer 24 formed between the first electrodes 20 and the second electrodes 22 for insulating the first electrodes 20 and the second electrodes 22, a first polarizer 26a on the bottom surface of the lower substrate 14, a second polarizer 26b on the upper surface of the upper substrate 12, a first alignment film 28a on the upper surface of the lower substrate 14, a second alignment film 28b on the bottom surface of the upper substrate 12, and a plurality of liquid crystal molecules 30 filled between the upper substrate 12 and the lower substrate 14. Any two adjoining scan lines 16 and any two adjoining data lines 18 are crossed to define a pixel.
The first electrodes 20 are common electrodes, and the second electrodes 22 are pixel electrodes. The first electrodes 20 contain a plurality of first electrode offshoots 20a, 20b, and 20c with equal distances and being parallel with the data lines 18. The first electrodes 20 are electrically connected to a common signal. The second electrodes 22 contain a plurality of second electrode offshoots 22a and 22b with equal distances. The second electrode offshoots 22a and 22b are parallel with the first electrode offshoots 20a, 20b, and 20c. As shown in FIG. 2, the second electrode offshoot 22a is electrically connected to a thin film transistor (TFT) set on the crossover region of the data line 18 and the scan lines 16 for controlling the switching state of the pixel of the LCD 10.
Although the IPS-LCD can improve the performance of view angle of conventional TN-LCDs, another problem still exists in an IPS-LCD: a viewer in different view angles may see different color tones, especially when in a wider view angle. This is because a liquid crystal molecule has an elongated shape with an elongated major axis and a minor axis, so that it has a property of anisotropic refraction. This results in the viewer not seeing exactly the same color tones in different positions or directions. Therefore a Super In-plane Switching mode LCD (Super-IPS LCD) is developed.
FIG. 3 is a top view of a lower substrate 52 of a Super-IPS LCD 50 according to the prior art. Referring to FIG. 3, the lower substrate 52 of the Super-IPS LCD 50 according to the prior art contains a plurality of parallel scan lines 54 and a plurality of data lines 56 with equal distances. The scan lines 54 and the data lines 56 are arranged in a crossing manner to form a pixel matrix. Any two of the adjoining scan lines 54 and any two of the adjoining data lines 56 are crossed to define a pixel 58. In addition, at least one switching device 60, such as a TFT, is set in each of the crossover region of the scan lines 54 and the data lines 56. A common electrode 62 containing a plurality of parallel common electrode offshoots 62a, 62b, 62c, and a pixel electrode 64 containing a plurality of pixel electrode offshoots 64a, 64b parallel with the common electrode offshoots 62a, 62b, 62c are disposed on the lower substrate 52 of each of the pixel 58.
In contrast to the conventional IPS-LCD 10, the data lines 56, the common electrode offshoots 62a, 62b, 62c, and the pixel electrode offshoots 64a, 64b of the Super-IPS LCD 50 are shown as bended lines or curved lines. Therefore the common electrode offshoots 62a, 62b, 62c, and the pixel electrode offshoots 64a, 64b with different directions in a pixel 58 produce electric fields with different directions, which make the liquid crystal molecules in the pixel 58 deflect to different directions to solve the problem of un-balanced color tones of the conventional IPS-LCD 10.
In both of the IPS-LCD and the Super-IPS LCD according to the prior art, the pixel electrodes, the scan lines below the pixel electrodes, and the insulation layer between the pixel electrodes and the scan lines (such as the insulation layer 24 in FIG. 1) serve together as storage capacitors for storing the electricity to make the liquid crystal molecules deflect. Taking the Super-IPS LCD 50 as an example, the pixel electrode 64, the scan line 54, and the insulation layer set between the pixel electrode 64 and the scan line 54 serve together as a storage capacitor of the pixel 58. As a result, the pixel electrode in each of the pixels of a conventional LCD has to be designed in particular to cover an adjacent scan line to form a storage capacitor. In order to store sufficient electricity to supply the LCD showing an image, the overlapping portion of the pixel electrode and the scan line must occupy a certain extent area. Thus a pixel electrode should occupy a large area of the pixel, and each of the scan lines also should be wide to satisfy the condition of being a storage capacitor of the pixel. Besides, both of the pixel electrodes and the scan lines are formed by non-transparent metal materials, therefore light beams cannot not pass through the wide pixel electrodes and scan lines, which means the LCD is limited to lower opening ratio. In the modern technology, it is difficult to fabricate an LCD with a low opening ratio to become lighter and thinner. An LCD with a low opening ratio also need higher fabricating cost, which makes the manufacturer less competitive in the LCD market.
As a result, to fabricate an LCD with a high opening ratio without difficult fabricating processes to raise the competitive superiority is an important issue.